Despite widespread recognition about the harmful health effects of smoking and decreases in smoking in the general population, as many as 70 percent of individuals with serious mental illness (SMI) smoke cigarettes. Smoking is a primary cause of the excess mortality of persons with SMI. Interventions that have been developed to treat smoking in persons with SMI show promise, but quit rates are modest and such interventions have not been optimized to include a well-specified peer support component. Peer support is well established in the treatment of other addictions and has assumed an important role in mental health services in general. Peer support is particularly important in smoking cessation because of the strong connection that has been demonstrated in the general population between quitting smoking and interpersonal associations with non-smokers. A peer support program by persons with SMI who have successfully quit smoking thus represents a logical approach to be added to smoking cessation interventions. Our first aim is to design a well-specified peer mentor program that will enhance a professionally led behavioral group intervention for smoking cessation for persons with SMI that we previously developed. Based on social cognitive theory, the proposed peer program will provide modeling and encouragement in order to increase engagement in and social support for smoking cessation, factors which are associated with achieving abstinence. We will also design a curriculum to train potential peer mentors for this role. Our second aim is to refine the procedural and training manuals for the peer mentor program after an initial pre-pilot study. We will train qualified mental health consumers who have successfully quit smoking to serve as peer mentors, evaluate their response to the training, and then employ them to implement the peer mentor program with smokers in conjunction with the standardized group intervention for smoking cessation. In our third aim, we will evaluate the revised peer mentor program in a carefully monitored pilot trial at two clinical sites with a larger number of peer mentors and smokers. We will again monitor the fidelity with which the peer intervention is delivered and its feasibility and acceptability. We will study in detail the peer mentors' experience and the responses of the smoking participants. We will measure the smoking outcomes of the participants and evaluate potential mediators of smoking outcomes related to the peer mentor intervention including the participant's alliance with, and perceived social support for smoking cessation from, the peer, in preparation for a future randomized trial. At the conclusion of this innovative study, we will have produced and evaluated a peer mentor program and accompanying training curriculum that can be further tested and applied to other smoking cessation interventions and which has the potential to fill an important gap in existing interventions. By seeking to improve the treatment of nicotine addiction in persons with SMI, our proposal contributes to the NIDA objective of developing more effective treatments for addiction in association with co-morbid conditions.